This structure represents 3 pools of locks, aws, ping-pong-tables, and
vsphere. The .gitkeep files are required to keep the unclaimed and
claimed directories track-able by Git if there are no files in them.

You will need to mirror this structure in your own lock repository. In other words, initialize an empty repository
and create one directory in the root of the repository for each pool of locks (e.g. aws). Inside of each lock pool directory, create one directory
named claimed and one directory named unclaimed. Inside each claimed and unclaimed directory, create an empty
filed named .gitkeep. Finally, create individual locks by making an empty file inside of the unclaimed directory
(assuming you want your lock to be unclaimed by default) with the desired name of the lock (e.g. env-1).

Source Configuration

uri: Required. The location of the repository.

branch: Required. The branch to track.

pool: Required. The logical name of your pool of things to lock.

private_key: Optional. Private key to use when pulling/pushing. Ensure it does not require a password.
Example:

username: Optional. Username for HTTP(S) auth when pulling/pushing.
This is needed when only HTTP/HTTPS protocol for git is available (which does not support private key auth) and auth is required.

password: Optional. Password for HTTP(S) auth when pulling/pushing.

retry_delay: Optional. If specified, dictates how long to wait until
retrying to acquire a lock or release a lock. The default is 10 seconds.
Valid values: 60s, 90m, 1h.

Behavior

check: Check for changes to the pool.

The repository is cloned (or pulled if already present), and any commits made to the specified pool from the given version on are returned. If no version is
given, the ref for HEAD is returned.

in: Fetch an acquired lock.

Outputs 2 files:

metadata: Contains the contents of whatever was in your lock file. This is
useful for environment configuration settings.

name: Contains the name of lock that was acquired.

out: Acquire, release, add, or remove a lock.

Performs one of the following actions to change the state of the pool.

Parameters

One of the following is required.

acquire: If true, we will attempt to move a randomly chosen lock from the
pool's unclaimed directory to the claimed directory. Acquiring will retry
until a lock becomes available.

claim: If set, the specified lock from the pool will be acquired, rather
than a random one (as in acquire). Like acquire, claiming will retry
until the specific lock becomes available.

release: If set, we will release the lock by moving it from claimed to
unclaimed. The value is the path of the lock to release (a directory
containing name and metadata), which typically is just the step that
provided the lock (either a get to pass one along or a put to acquire).

Note: the lock must be available in your job before you can release it. In
other words, a get step to fetch metadata about the lock is necessary
before a put step can release the lock.

add: If set, we will add a new lock to the pool in the unclaimed state. The
value is the path to a directory containing the files name and metadata
which should contain the name of your new lock and the contents you would like
in the lock, respectively.

add_claimed: Exactly the same as the add param, but adds a lock to the
pool in the claimed state.

remove: If set, we will remove the given lock from the pool. The value is
the same as release. This can be used for e.g. tearing down an environment,
or moving a lock between pools by using add with a different pool in a
second step.

update: If set, we will update an existing lock in the pool.

If the existing lock is in the unclaimed state we will update it with the
contents of the metadata file.

If no such lock is present in either the claimed or unclaimed state we add a
new lock to the pool in the unclaimed state.

If the lock is in the claimed state we will wait for it to be unclaimed and
proceed to update it as above.

The value is the path to a directory containing the files name and
metadata which should contain the name of your new lock and the contents you
would like in the lock, respectively.

Example Concourse Configuration

The following example pipeline models acquiring, passing through, and releasing
a lock based on the example git repository structure:

Managing multiple locks

The parameter for release is the name of the step whose lock to release.
Normally this is just the same as the name of the resource, but if you have
custom names for put (for example if you need to acquire multiple instances
of the same pool), you would put that name instead. For example:

Development

Prerequisites

golang is required - version 1.9.x is tested; earlier versions may also
work.

docker is required - version 17.06.x is tested; earlier versions may also
work.

Running the tests

The tests have been embedded with the Dockerfile; ensuring that the testing
environment is consistent across any docker enabled platform. When the docker
image builds, the test are run inside the docker container, on failure they
will stop the build.

Run the tests with the following command:

docker build -t pool-resource .

Contributing

Please make all pull requests to the master branch and ensure tests pass
locally.